1. Field of the Invention
The present invention generally relates to a mobile electronic system, and more particularly, to a mobile electronic device and a charging accessory.
2. Description of Related Art
A mobile phone needs to be charged frequently. A conventional adapter or the latest universal serial bus (USB) charging mechanism can be adopted for charging a mobile phone.
As shown in FIG. 1, the mobile phone 100 includes a charging circuit 110 and a battery 120. The mobile phone 100 receives a charging voltage from a USB cable 130 to charge the battery 120. The standard charging voltage supplied by a USB is 5 volts. However, the rated voltage of the battery 120 may not be 5 volts. Instead, the rated voltage of the battery 120 may be 3 volts, 3.5 volts, or 4 volts. The charging circuit 110 detects an instantaneous voltage 125 of the battery 120 and converts the charging voltage (5 volts) supplied by the USB cable 130 into a suitable voltage according to the instantaneous voltage 125 to charge the battery 120.
As to a user, the faster a mobile phone is charged, the better. However, a quick charge requires the charging circuit to supply a large enough charging current. With the limited heat dissipation capability and internal space of any existing mobile phone, the charging current supplied by the charging circuit of the mobile phone is not very large (usually no more than 1 ampere), which therefore is insufficient for satisfying the user's demand for quick charge.
In addition, the problem of insufficient charging voltage also exists in mobile phones. For example, assuming that the voltage supplied by the USB cable 130 comes with an offset and actually 4.95 volts is supplied by the USB cable 130, and the charging voltage required by the battery 120 is 4.35 volts, in order to quickly charge the battery 120, the charging circuit 110 has to supply a current of 3 amperes. It can be understood through calculation that the voltage drop from the USB cable 130 to the battery 120 has to be equal to or smaller than 0.6 volts. Namely, the resistance from the USB cable 130 to the battery 120 has to be equal to or smaller than 200 milliohms. However, because the USB cable 130 usually has a resistance of 300 milliohms and the charging circuit 110 usually has a resistance of 100 milliohms, the total resistance (400 milliohms) exceeds the tolerable upper limit. This is one of the problems to be resolved in order to quickly charge a mobile phone.